A10 Overview Critters.ppt - Department of Computer Science · &rs\uljkw e\ 3hduvrq (gxfdwlrq )rrg 6lpxodwru sodfhv irrg udqgrpo\ durxqg zruog (dwlqj irrg lqfuhdvhv vfruh iru vshflhv

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Copyright 2010 by Pearson Education1

Assignment 11:Critters

reading: HW11 assignment spec


Critters A simulation world with animal objects with behavior:

fight animal fighting getColor color to display getMove movement toString letter to display eat eat food?

You must implement: Ant

Bird

Vulture

Hippo

Longhorn (Wins and Creative)



FoodSimulator places food randomly around world

Eating food increases score for species, but …

Critters sleep after eatingsimulator (CritterMain) handles this

A Critter that gets in a fight while sleeping always losessimulator handles this


A Critter classpublic class name extends Critter {

...

}

extends Critter tells the simulator your class is a critter

override methods from Critter based on Critter spec Critter has a number of methods not required by the 4

simple Critter classes (Ant, Bird, Vulture, Hippo) … but you should use them to create a killer Longhorn


ScoringScore for each species:

For all animals of that species

Number of animals alive

Number of fights won

Pieces of food eaten


Mating Two Critters of same species next to each

other mate and produce a baby Critter

Simulator handles this

Critters not asked if they want to mate

Critters vulnerable while mating (heart graphic indicates mating) automatically lose fight

The Simulator handles all of this You don't write any code to deal with mating


Critter Class


Enums Critter class has two nested Enums for

Direction of movement and how to fight


Nested Enums To access a Direction or Attack a class external

to Critter would use the following syntax:

Critter.Direction.NORTH

Critter.ATTACK.POUNCE

Classes that are desecdants of Critter (like the ones you implement) do not have to use the Critter.

it is implicit

Direction.SOUTH, Attack.ROAR


How the simulator works When you press "Go", the simulator enters a loop:

move each animal once (getMove), in random order if the animal has moved onto an occupied square, fight!

Key concept: The simulator is in control, NOT your animal. Example: getMove can return only one move at a time.getMove can't use loops to return a sequence of moves. It wouldn't be fair to let one animal make many moves in one turn!

Your animal must keep state (as fields, instance variables) so that it can make a single move, and know what moves to make later.


Critter exercise: Stone Write a critter class Stone(the dumbest of all critters):

Method Behavior

constructor public Stone()

fight Always Attack.ROAR

getColor Always Color.GRAY

getMove Always Direction.CENTER

toString "S"

eat Always false


Ideas for state You must not only have the right state, but update that

state properly when relevant actions occur.

Counting is helpful: How many total moves has this animal made? How many times has it fought?

Remembering recent actions in fields is helpful: Which direction did the animal move last?

How many times has it moved that way?


Keeping state How can a critter move west until it fights?

public Direction getMove() {while (animal has not fought) {

return Direction.EAST;}while (animal has not fought a second time) {

return Direction.EAST;}

}

private int fights; // total times Critter has fought

public int getMove() {if (fights % 2 == 0) {

return Direction.WEST;} else {

return Direction.EAST;}

}


Testing critters Use the MiniMain to create String based on actions

and print those out

Focus on one specific critter of one specific type Only spawn 1 of each animal, for debugging

Make sure your fields update properly Use println statements to see field values

Look at the behavior one step at a time Use "Tick" rather than "Go"


Critter exercise: SnakeMethod Behavior

constructor public Snake(boolean northSnake)

fight alternates between SCRATCH and POUNCEgetColor Yellow

getMove north snakes: 5 steps north, pause 5 ticks, 5 steps north, pause 5 ticks, …

otherwise:5 steps west, pause 5 ticks, 5 steps west, pause 5 ticks, …

eat always eatstoString "K"


Determining necessary fields Information required to decide what move to make?

Direction to go in Length of current cycle Number of moves made in current cycle

Remembering things you've done in the past: an int counter? a boolean flag?

Documents

A10 Overview Critters.ppt - Department of Computer Science · &rs\uljkw e\ 3hduvrq (gxfdwlrq )rrg 6lpxodwru sodfhv irrg udqgrpo\ durxqg zruog (dwlqj irrg lqfuhdvhv vfruh iru vshflhv